Natural gas is a kind of high calorific and clean energy. With the increasingly serious environmental pollution and the discovery and development of a large number of gas fields, natural gas accounts for a higher proportion in the global energy market. Natural gas can be transported in a variety of ways, such as liquefied natural gas (LNG), canned compressed natural gas (CNG) and pipeline compressed natural gas (PNG). Its core is to increase the density (liquid or high-pressure gas) to enhance the efficiency of transportation.
Pipeline natural gas (including associated gas produced from oil field) from the mine field or treatment plant is transported to the city gas distribution center or the tube of industrial enterprise users, which is also called gas pipeline. Natural gas that is transported over long distances in pipelines is called pipeline natural gas (PNG). In the process of long-distance natural gas pipeline transportation, the transportation cost can be reduced due to the increase of gas pressure. The pipeline design transport pressure is generally around 10 Mpa or even higher. Compressed natural gas (CNG) is low-pressure natural gas compressed to 20-25 MPa then send into a set of high-pressure-resistant gas cylinders or pipe bundles by compressor. The effect of compression is to increase its density. It allows more natural gas to be transported and is more suitable for long-distance transportation to instead of long-distance pipeline transportation. The main component of natural gas is methane. When the temperature drops down to about −162° C. at the atmospheric pressure, the gas turn to liquid state, referred to as Liquid Natural Gas (LNG). Since the density of LNG is about 625 times to natural gas at standard state, LNG takes many advantages such as easier storage and transportation, high safety, low investment and environmental-friendly. With the popularity of natural gas, many cities have set up large LNG city gate stations to receive, gasify, odorizing, metering and distribute natural gas for natural gas is gaseous state when it is used.